This invention relates to electrostatographic copying and more specifically to a method of recovering selenium and/or selenium alloys from endless xerographic belts.
The art of xerography involves the use of a photoconductive element, i.e. drum or plate, which is uniformly electrostatically charged in order to sensitize its surface. The plate is then exposed in an imagewise manner to activating electromagnetic radiation which selectively dissipates the charge in the exposed areas of the photoconductive material while leaving behind a latent electrostatic image in the non-exposed areas. This latent electrostatic image may then be developed by depositing a finely divided electroscopic marking material on the surface of the photoconductive material. This concept was originally disclosed by C. F. Carlson in U.S. Pat. No. 2,297,691 and is further amplified and described in many related patents.
Xerographic drums of a conductive substrate such as aluminum with a layer of a photoconductive material such as amorphous selenium on and in operative contact with its surface have been used for many years. More recently, the endless xerographic belt has been used in xerographic duplication. The endless xerographic belt must be flexible and is preferably seamless. Suitable belts are quite thin and have a surface with a high degree of smoothness due to the need for the production of high quality images on the image retention side of the belt. A further requirement is that the belt have a relatively high tensile strength. Satisfactory belts can be prepared by electroplating a ductile metal, e.g., stainless steel, brass, aluminum or nickel, onto a mandrel to form a thin, uniform layer of the metal. Removal of the metal layer from the mandrel provides the substrate upon which the photoconductive material can be deposited to form the xerographic belt.
Xerographic photoreceptors, whether they be in the form of a drum or belt, normally have a barrier layer between the conductive substrate and the layer of photoconductive material to prevent charge injection from the conductive substrate in the dark. When the substrate used is an aluminum drum, a thin layer of aluminum oxide, formed by oxidizing the surface of the drum, serves well as the blocking layer. When the substrate is an endless belt, it has been found that a thin, normally sub-micron layer of an insulating organic resin is desirable for use as the blocking layer. Typically, the organic barrier layer used is a polymer blend of a polycarbonate and polyurethane resins in a ratio of about 7 parts by weight polycarbonate to 1 part by weight polyurethane. After application of the organic blocking material to the substrate, amorphous selenium or an alloy thereof is applied by vacuum deposition.
Belts made in this manner serve admirably in high speed xerographic duplicators but, of course, wear out over extended periods of use. When a belt wears out, sound economics dictates that the selenium or selenium alloy be recovered and recycled. Various methods are available for stripping selenium from the substrate. These include heat stripping, water quenching, ultrasonics and bead blasting. These processes, however, are not readily adaptable to the previously described xerographic belt because of the presence of the organic interface on the flexible metal substrate. Stripping selenium by these processes also strips part of the organic material thereby contaminating the recovered selenium. Cold shocking the belt, such as by dipping it in liquid nitrogen, removes the selenium without affecting the organic interface, but is inherently a two step process; the first step being a liquid nitrogen dip and the second step consisting of mechanical vibration or shaking.
It would be desirable, and it is an object of the present invention, to provide a novel method for recovering selenium or selenium alloy from the surface of a xerographic belt comprising a ductile metal substrate having a thin layer of an organic resinous material on its surface which is in turn overcoated with selenium.
A further object is to provide such a process which yields recovered selenium of high purity which is not contaminated with the organic resinous material.
An additional object is to provide such a process which strips the selenium from the belt in a single step.